1. Field of the Invention
This invention relates to an improvement in a cracking process designed for use of an entirely amorphous cracking catalyst. The improvement resides in product of increased gasoline quality and octane number being obtained while not significantly affecting total yield in catalytic cracking units which are designed to utilize in the normal course an amorphous catalyst. The improved process involves operation of said cracking process with a cracking catalyst which is only from about 0.01 to about 25 weight percent crystalline zeolite of a particular type, the remainder being the conventional amorphous cracking catalyst component normally used in the process. The crystalline zeolite component may be included in the otherwise amorphous catalyst composition or may be added to the amorphous catalyst inventory by means of separate additive composition comprising the crystallic zeolite to provide the minor amount of said zeolite therein.
2. Description of the Prior Art
Hydrocarbon conversion processes utilizing crystalline zeolites have been the subject of extensive investigation during recent years, as is clear from both the patent and scientific literature. Crystalline zeolites have been found to be particularly effective for a wide variety of hydrocarbon conversion processes including the catalytic cracking of a gas oil to produce motor fuels and have been described and claimed in many patents, including U.S. Pat. Nos. 3,140,249; 3,140,251; 3,140,252; 3,140,253; and 3,271,418. It is also known in the prior art to incorporate the crystalline zeolite into a matrix for catalytic cracking and such disclosure appears in one or more of the above-identified U.S. patents.
It is also known that improved results will be obtained with regard to the catalytic cracking of gas oils if a crystalline zeolite having a pore size of less than 7 Angstrom units is included with a crystalline zeolite having a pore size greater than 8 Angstrom units, either with or without a matrix. A disclosure of this type is found in U.S. Pat. No. 3,769,202. Although the incorporation of a crystalline zeolite having a pore size of less than 7 Angstrom units into a catalyst composite comprising a larger pore size crystalline zeolite (pore size greater than 8 Angstrom units) has indeed been very effective with respect to the raising of octane number, nevertheless it did so at the expense of the overall yield of gasoline.
Improved results in catalytic cracking with respect to both octane number and overall yield achieved in U.S. Pat. No. 3,758,403. In said patent, the cracking catalyst was comprised of a large pore size crystalline zeolite (pore size greater than 7 Angstrom units) in admixture with ZSM-5 type zeolite wherein the ratio of ZSM-5type zeolite to large pore size crystalline zeolite was in the range of 1:10 to 3:1.
The use of ZSM-5 type zeolite in conjunction with a zeolite cracking catalyst of the X or Y faujasite variety is described in U.S. Pat. Nos. 3,894,931; 3,894,933; and 3,894,934. The two former patents disclose the use of ZSM-5 type zeolite in amounts up to and about 5 to 10 weight percent; the latter patent discloses the weight ratio of ZSM-5 type zeolite to large pore size crystalline zeolite in the range of 1:10 to 3:1.
It is extremely desirable to provide a process which will provide high octane unleaded gasoline without undue sacrifice of gasoline yield for the refiner operating a cracking process utilizing an entirely amorphous cracking catalyst. It is even more desirable if such results could be obtained in conjunction with an increase in operational flexibility and without undue use of expensive catalysts.
The criticality of using only small amounts of catalyst comprising ZSM-5 class zeolite to achieve improved results with respect to overall product quality and octane number while not significantly affecting yield in a cracking process utilizing an inventory of otherwise amorphous cracking catalyst has heretofore not been recognized in the art. It is the basis of the present invention that the addition of only small quantities of zeolite ZSM-5 type crystalline material to an entirely amorphous cracking catalyst inventory in the process designed for said amorphous catalyst will give these beneficial results. It is to be understood that to obtain these beneficial results the ZSM-5 type zeolite may be included in the otherwise amorphous catalyst composition or, in a preferred embodiment, may be added to the amorphous cracking catalyst inventory by means of separate additive composition comprising the ZSM-5 type zeolite. Such method would provide the refiner increase operational flexibility since only a small quantity of additive composition can improve the octane number of the gasoline product significantly.
It is noted that U.S. Pat. Nos. Re. 29,857 and 3,926,782 suggest the use of zeolite ZSM-5 as a cracking catalyst component in an amount from 1 to 90 weight percent with a matrix. Specific catalytic cracking processes are taught in U.S. Pat. Nos. 3,748,251; 3,894,933; 3,951,781 and 4,002,552. These processes use zeolite cracking catalysts, in general, and zeolite ZSM-5 specifically in varying amounts in catalyst compositions to provide various results.